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  • C12Q—MEASURING OR TESTING PROCESSES INVOLVING ENZYMES, NUCLEIC ACIDS OR MICROORGANISMS; COMPOSITIONS OR TEST PAPERS THEREFOR; PROCESSES OF PREPARING SUCH COMPOSITIONS; CONDITION-RESPONSIVE CONTROL IN MICROBIOLOGICAL OR ENZYMOLOGICAL PROCESSES
  • C12Q1/00—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions
  • C12Q1/68—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions involving nucleic acids
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12Q—MEASURING OR TESTING PROCESSES INVOLVING ENZYMES, NUCLEIC ACIDS OR MICROORGANISMS; COMPOSITIONS OR TEST PAPERS THEREFOR; PROCESSES OF PREPARING SUCH COMPOSITIONS; CONDITION-RESPONSIVE CONTROL IN MICROBIOLOGICAL OR ENZYMOLOGICAL PROCESSES
  • C12Q1/00—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions
  • C12Q1/68—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions involving nucleic acids
  • C12Q1/6876—Nucleic acid products used in the analysis of nucleic acids, e.g. primers or probes
  • C12Q1/6888—Nucleic acid products used in the analysis of nucleic acids, e.g. primers or probes for detection or identification of organisms
  • C12Q1/689—Nucleic acid products used in the analysis of nucleic acids, e.g. primers or probes for detection or identification of organisms for bacteria

Definitions

• oligonucleotides targeted to Mycoplasma pneumoniae nucleic acid.
• Different types of oligonucleotides are described including hybridization assay probes, helper probes, and amplification oligonucleotides.
• the oligonucleotides are particularly useful for detecting the species Mycoplasma pneumoniae in test samples, such as from throat swabs, tissue samples, body fluids, experimental solutions and cultures.
• Single strands of deoxyribo- ("DNA”) or ribo-("RNA") nucleic acid formed from nucleotides including the bases adenine (A), cytosine (C), thymidine (T), guanine (G), uracil (U), or inosine (I), may hybridize to form a double-stranded structure held together by hydrogen bonds between pairs of complementary bases.
• A is hydrogen bonded to T or U
• G or I are hydrogen bonded to C.
• classical base pairs AT or AU, TA or UA, GC, or CG are present. Additionally, some mismatched base pairs (e.g., AG, GU) may be present.
• Mycoplasma pneumoniae is a prokaryote in the taxonomic Mollicutes class. Mollicutes lack a bacterial cell wall and have a small genome size. They are considered some of the smallest of the free-living microorganisms. Mycoplasma pneumoniae is a primary pathogen of man that produces acute respiratory disease. It is the most common cause of atypical pneumonia and is responsible for 15-20% of all pneumonia cases.
• DNA hybridization assay probes directed to genomic sequences for detecting Mycoplasma pneumoniae are mentioned by Hyman et al., J. Clin. Microbiol. 25:726-728 (1987), Buck et al., J. Clin. Microbiol. 30:3280-3283 (1992), and Bernet et al., J. Clin. Microbiol. 27:2492-2495 (1989).
• Probes directed to ribosomal RNA (rRNA) sequences of Mycoplasma pneumoniae are mentioned by Tilton (Diagn. Microbiol. Infec. Dis. 10:109-112 (1988), Yogev et al., J. Clin. Microbiol. 26:1198-1201, (1988), Gobel et al., J.
• the present invention describes oligonucleotides targeted to Mycoplasma pneumoniae nucleic acid sequences which are particularly useful to aid in detecting Mycoplasma pneumoniae.
• the oligonucleotides can aid in detecting Mycoplasma pneumoniae in different ways such as by acting as hybridization assay probes, helper probes, and/or amplification primers.
• Hybridization assay probes can preferentially hybridize to a Mycoplasma pneumoniae nucleic acid target region to form a detectable duplex indicating the presence of Mycoplasma pneumoniae.
• Helper probes can hybridize to a Mycoplasma pneumoniae nucleic acid target region under stringent hybridization assay conditions and can be used to enhance the formation of a hybridization assay probe:target nucleic acid duplex.
• Amplification primers can hybridize to a Mycoplasma pneumoniae target region under amplification conditions and can be used as a primers in amplification reactions producing Mycoplasma pneumoniae nucleic acid.
• Hybridization assay probes and helper probes contain a targeted nucleic acid region having a nucleotide sequence complementary, or substantially complementary to a target sequence.
• the hybridization assay probes may also have additional nucleotides outside of the targeted nucleic acid region which are complementary or not complementary to Mycoplasma pneumoniae nucleic acid.
• Hybridization assay probes are preferably 12-100 nucleotides in length and the targeted nucleic acid region is substantially similar to a nucleotide sequence perfectly complementary to a target sequence.
• a substantially similar nucleotide sequence is a nucleotide sequence identical to, or having no more than a 20% nucleotide base difference excluding RNA or DNA equivalent nucleotides than an identified nucleotide sequence and which enables an oligonucleotide to preferentially hybridize to rRNA or rDNA of Mycoplasma pneumoniae, over rRNA or rDNA of one or more closely related organism.
• Organisms closely related to Mycoplasma pneumoniae include Mycoplasma genitalium, Mycoplasma orale, Mycoplasma buccale, Mycoplasma faucium, and Mycoplasma salivarium. Preferential hybridization can occur under stringent hybridization assay conditions.
• substantially similar refers to a 10% difference and a 5% difference to a particular nucleotide sequence.
• RNA and DNA equivalents refer to RNA and DNA molecules having the same complementary base pair hybridization properties. RNA and DNA equivalents have different sugar groups (i.e., ribose versus deoxyribose), and may differ by the presence of uracil in RNA and thymine in DNA. The difference between RNA and DNA equivalents do not contribute to differences in substantially corresponding nucleic acid sequences because the equivalents have the same degree of complementarity to a particular sequence.
• Mycoplasma genitalium appears to be the most closely related Mycoplasma to Mycoplasma pneumoniae and has a very similar rRNA sequence to Mycoplasma pneumoniae rRNA. Because of the greater phylogenetic divergence occurring between more distant organisms, hybridization assay probes able to distinguish Mycoplasma pneumoniae from Mycoplasma genitalium also distinguish Mycoplasma pneumoniae from non-related microorganisms and preferably other more distantly related Mycoplasma. Thus, hybridization assay probes able to distinguish the presence of Mycoplasma pneumoniae from Mycoplasma genitalium are useful for detecting Mycoplasma pneumoniae.
• Species of Mycoplasma found in humans include Mycoplasma pneumoniae, Mycoplasma genitalium, Mycoplasma orale, Mycoplasma buccale, Mycoplasma faucium, and Mycoplasma salivarium.
• hybridization assay probes preferentially hybridize to Mycoplasma pneumoniae nucleic acid over one or more, more preferably all, nucleic acids present in microorganisms selected from the group consisting of Mycoplasma genitalium, Mycoplasma orale, Mycoplasma buccale, Mycoplasma faucium and Mycoplasma salivarium.
• a first aspect of the present invention describes hybridization assay probes able to preferentially hybridize to a Mycoplasma pneumoniae target nucleic acid sequence region.
• the hybridization assay probes have a targeted nucleic acid sequence complementary to ribosomal RNA (rRNA) or DNA (rDNA) of Mycoplasma pneumoniae target sequence.
• the hybridization assay probes are at least 90 % complementary, preferably perfectly complementary, to at least a portion of the described target sequence region. The portion is at least 10 nucleotides in length and preferably at least 18 nucleotides in length.
• hybridization assay probes can hybridize to their target nucleic acids to form stable probe:target hybrids indicating the presence of the target nucleic acid and does not form a sufficient number of stable probe:non-target hybrids to indicate the presence of a closely related non-target nucleic acid.
• the probe hybridizes to target nucleic acid to a sufficiently greater extent than to non-target nucleic acid to enable one skilled in the art to accurately detect the presence of Mycoplasma pneumoniae and distinguish its presence from that of a closely related organism.
• Preferential hybridization can be measured using techniques known in the art and described herein, such as in the examples provided below.
• there is at least a 100 fold difference between target and non-target hybridization signals more preferably at least a 1,000 fold difference, more preferably at least a 10,000 fold difference.
• non-target hybridization signals are no more than background level.
• target nucleic acid sequence region refers to a nucleic acid sequence present in Mycoplasma pneumoniae nucleic acid or a sequence complementary thereto, which is not present in a closely related Mycoplasma species nucleic acid.
• Nucleic acids having nucleotide sequences complementary to a target sequence may be generated by target amplification techniques such as polymerase chain reaction (PCR) or transcription mediated amplification (e.g., Kacian and Fultz, Nucleic Acid Amplification Methods., EPO application number 90307503.4).
• PCR polymerase chain reaction
• transcription mediated amplification e.g., Kacian and Fultz, Nucleic Acid Amplification Methods., EPO application number 90307503.4.
• hybridization assay probes 18-100 nucleotides in length which comprise, consist essentially of, consist of, or have a nucleotide sequence substantially similar to, the sequences (written 5' to 3'):
• oligonucleotides complementary thereto SEQ. ID. NOs. 21, 24, 27, 30, 33, 36, 39, 42, and 87
• RNA equivalents having uracil substituted for thymine SEQ. ID. NOs: 22, 25, 28, 31, 34, 37, 40, 43 and 88
• RNA equivalents of the oligonucleotides complementary thereto, having uracil substituted for thymine SEQ. ID. NOs: 23, 26, 29, 32, 35, 8, 41, 44, and 89).
• probes are complementary to a target region present in rRNA and/or rDNA which varies between Mycoplasma pneumoniae and Mycoplasma genitalium.
• the probes can hybridize to Mycoplasma pneumoniae nucleic acid and distinguish Mycoplasma pneumoniae from a closely related Mycoplasma and are useful for detecting the presence of Mycoplasma pneumoniae.
• the probes may be used to determine the quantity of Mycoplasma pneumoniae present in a sample.
• helper oligonucleotides can have a targeted region having a nucleotide sequence perfectly complementary to at least 10 contiguous nucleic acids present in a helper target nucleotide sequence selected from the group consisting of:
• Helper probes can be used to facilitate hybridization of a hybridization assay probe to its target nucleic acid sequence. Helper probes facilitate hybridization by enhancing the kinetics and/or the T m of the target:hybridization probe duplex. Helper probes are generally described in Hogan and Milliman, U.S. Pat. No. 5,030,557, which is hereby incorporated by reference herein.
• helper probes are oligonucleotides which have, consist essentially of, or consist of, the following nucleotide sequences (written 5'-3'):
• the helper probe can hybridize to the same target nucleic acid as a hybridization assay probe and are preferably 12 to 100 nucleotide in length, more preferably 18 to 50 nucleotide in length.
• oligonucleotides can be used alternatively as a hybridization assay probe or a helper probe.
• examples of such oligonucleotides are those having the nucleotide sequence of SEQ. ID. Nos. 5, 6, or 7.
• probe mixes for detecting Mycoplasma pneumoniae under stringent hybridization assay conditions.
• the probe mix contains a hybridization assay probe and at least one helper probe.
• different hybridization assay probe and helper probe combinations are described.
• compositions comprising a nucleic acid hybrid.
• the hybrid is made up of a hybridization assay probe and a nucleic acid molecule having a nucleic acid sequence substantially complementary thereto.
• One use of the formed hybrid is to detect the presence of a target sequence.
• acridinium ester (“AE") present in hybrids is resistant to hydrolysis in alkali solution while acridinium ester present in single-stranded nucleic acid is hydrolyzed in alkali solution (Arnold et al., entitled “Homogeneous Protection Assay," EPO application number 88308767.8, publication number 309230, hereby incorporated by reference herein).
• binding of AE-labeled probe to target can be detected, after hydrolysis of the unbound AE-labeled probe, by measuring chemiluminescence of acridinium ester remaining in the nucleic acid hybrid.
• the invention features amplification oligonucleotides useful for amplifying Mycoplsma pneumoniae target regions.
• Amplification oligonucleotides preferably have or consist essentially of the following nucleotide sequences:
• RNA equivalents having uracil substituted for thymine SEQ. ID. NOs. 53, 61, 90, and 91.
• Amplification oligonucleotides are preferably 12 to 100 nucleotides in length, more preferably 18 to 50.
• Amplification oligonucleotides sequences may have modifications, such as blocked 3' and/or 5' termini or additions including, but not limited to, specific nucleic acid sequences recognized by an RNA polymerase, (e.g., the promoter sequence for T7, T3, or SP6 RNA polymerase); sequences enhancing initiation or elongation of RNA transcription by an RNA polymerase; or sequences providing for intramolecular base pairing and encouraging the formation of secondary or tertiary nucleic acid structures.
• RNA polymerase e.g., the promoter sequence for T7, T3, or SP6 RNA polymerase
• sequences enhancing initiation or elongation of RNA transcription by an RNA polymerase e.g., the promoter sequence for T7, T3, or SP6 RNA polymerase
• sequences enhancing initiation or elongation of RNA transcription by an RNA polymerase
• sequences providing for intramolecular base pairing and encouraging the formation of secondary or
• Amplification oligonucleotides can be used in nucleic acid amplification procedures, such as the polymerase chain reaction or an amplification reaction using RNA polymerase, DNA polymerase and RNase H or its equivalent, as described by Kacian and Fultz supra, and by Sninsky et al., U.S. Pat. No. 5,079,351; both references hereby incorporated by reference herein.
• methods are described for using the hybridization assay probes, helper probes, and amplification oligonucleotides. These methods are particularly useful to test samples obtained from human specimens for the presence of Mycoplasma pneumoniae.
• oligonucleotides and their use described herein offer a rapid, objective method of identifying and quantitating the presence of specific rRNA sequences unique to Mycoplasma pneumoniae in a test sample.
• Target nucleotide sequences useful for designing hybridization assay probes, amplification oligonucleotides, and/or helper probes are described herein.
• Target nucleotide sequences for hybridization assay probes are present in Mycoplasma pneumoniae nucleic acids but not the nucleic acids of closely related organisms.
• the identification of the target sequences, in addition to being useful for designing probes to detect Mycoplasma pneumoniae, also provides a basis for designing oligonucleotides to inhibit the growth of Mycoplasma pneumoniae.
• oligonucleotides such as ribozymes and anti-sense oligonucleotides targeted to Mycoplasma pneumoniae nucleic acid needed for microbial growth should be able to inhibit activity of the nucleic acid, thereby inhibiting Mycoplasma pneumoniae growth.
• Such oligonucleotides can be used to therapeutically treat patients infected with Mycoplasma pneumoniae.
• a more detailed description of oligonucleotide anti-sense activity is provided in publications such as Helene, C. and Toulme, J. Biochimica et Bioplysica Acta 1049:99 (1990), and Uhlmann, E. and Peyman, A. Chemical Reviews 90:543 (1990).
• target nucleic acid is meant a nucleic acid comprising a target nucleic acid sequence.
• target nucleic acid sequence By “target nucleic acid sequence,” “target nucleotide sequence” or “target sequence” is meant a specific deoxyribonucleotide or ribonucleotide sequence, or the nucleic acid sequence perfectly complementary thereto.
• Stringent hybridization assay conditions refer to conditions wherein a hybridization assay probe preferentially hybridizes with target nucleic acid (preferably rRNA or rDNA of Mycoplasma pneumoniae) and not with nucleic acid derived from a closely related non-target microorganism. Stringent hybridization assay conditions may vary depending upon factors including the hybridization assay probe nucleotide sequence and length, closely related non-target sequences, and the target sequence. Hybridization conditions include the temperature and the composition of the hybridization reagents or solutions.
• oligonucleotide two or more nucleotide subunits covalently joined together.
• the sugar groups of the nucleotide subunits may be ribose, deoxyribose, or modified derivatives thereof such as O-methyl ribose.
• the nucleotide subunits may by joined by linkages such as phosphodiester linkages, modified linkages or by non-nucleotide moieties, that do not prevent hybridization of the oligonucleotide to its complementary target nucleotide sequence.
• Modified linkages include those linkages in which a standard phosphodiester linkage is replaced with a different linkage, such as a phosphorothioate linkage, or methylphosphonate linkage.
• probe an oligonucleotide having a nucleotide sequence sufficiently complementary to its target nucleic acid sequence to form a detectable hybrid oligonucleotide:target duplex under stringent hybridization assays conditions.
• a probe is an isolated nucleic acid.
• Probes may have additional nucleotides outside of the targeted region so long as such nucleotides do not prevent hybridization under stringent hybridization conditions, and in the case of hybridization assay probes do not prevent preferentially hybridization- Non-complementary sequence, such as a promotor sequence, a binding site for RNA transcription, a restriction endonuclease recognition site, or sequences which will confer a desired secondary or tertiary structure such as a catalytic active site can be used to facilitate detection and/or amplification.
• Oligonucleotide probes of a defined sequence may be produced by techniques known to those of ordinary skill in the art, such as by chemical synthesis, and by in vitro or in vivo expression from recombinant nucleic acid molecules. Probes are preferably 12 to 100 nucleotides in length, more preferably 18 to 50 nucleotides in length.
• a “hybridization assay probe” is an isolated nucleic acid which can preferentially hybridize to a target Mycoplasma Pneumoniae 5S, 16S, or 23S rRNA, or to the corresponding ribosomal DNA (“rDNA”) nucleic acid, or to a nucleic acid having a nucleotide sequence complementary to the target nucleic acid under stringent hybridization assay conditions.
• a hybridization assay probe is preferably labeled with a reporter group moiety such as a radioisotope, a fluorescent moiety, a chemiluminescent moiety, an enzyme, or a ligand, which can be used to detect or confirm probe hybridization to its target sequence.
• a hybridization assay probe is preferably between 12 and 100 nucleotides in length, more preferably between 18 and 50 nucleotides in length.
• isolated nucleic acid is meant an oligonucleotide or nucleic acid molecule which is present in a form not found in nature without human intervention (e.g., recombined with foreign nucleic acid, isolated, or purified to some extent).
• nucleic acid hybrid or “hybrid” is meant a stable nucleic acid structure comprising a double-stranded, hydrogen-bonded region, preferably 12 to 100 nucleotides in length, more preferably 18 to 50 nucleotides in length.
• the structure is sufficiently stable to be detected by means such as chemiluminescent or fluorescent light detection, autoradiography, or gel electrophoresis.
• hybrids include RNA:RNA, RNA:DNA, or DNA:DNA duplex molecules.
• amplification oligonucleotide is meant an isolated nucleic acid capable of hybridizing with a target nucleic acid and acting as a primer and/or a promoter for nucleic acid synthesis.
• the target nucleic acid strand is the template for nucleic acid synthesis.
• Promoters recognized by an RNA polymerase such as T7, T3 and SP6 RNA polymerase can be used for transcription-based amplification.
• An amplification oligonucleotide is preferably 12 to 100 nucleotides in length; more preferably 18 to 50 nucleotides in length.
• nucleic acid amplification or “target amplification” is meant increasing the number of nucleic acid molecules having at least one target nucleic acid sequence.
• negative sense is meant a nucleic acid molecule perfectly complementary to a reference (i.e., sense) nucleic acid molecule.
• phrases "consist essentially of” or “consisting essentially of” means that the oligonucleotide has a nucleotide sequence substantially similar to a specified nucleotide sequence and may be up to four additional nucleotides longer or have two deleted nucleotides. Thus, these phrases contain both a sequence length limitation and a sequence variation limitation. Any additions or deletions are non-material variations of the specified nucleotide sequence which do not prevent the oligonucleotide from having its claimed property, such as being able to preferentially hybridize under stringent hybridization assay conditions to its target nucleic acid over non-target nucleic acids.
• the oligonucleotide may contain a nucleotide sequence substantially similar to a specified nucleic acid sequence without any additions or deletions.
• nucleic acids having a sufficient amount of contiguous complementary nucleotides to form, under stringent hybridization assay conditions, a hybrid stable for detection.
• hybridization assay probes can detect Mycoplasma pneumoniae and preferably distinguish it from the known and presumably most closely related taxonomic or phylogenetic neighbors and more distantly related organisms.
• Helper probes can be used to facilitate the hybridization of a hybridization assay probe to its target nucleotide sequence region.
• Amplification oligonucleotide can act as primers and may be part of promoter-primer combinations (i.e., a primer having an attached promoter sequence) to amplify a Mycoplasma pneumoniae target sequence.
• Prokaryotic organisms (excluding viruses) contain rDNA genes encoding 5S rRNA, 16S rRNA and 23S rRNA. Partial or full rRNA sequences of Mycoplasma pneumoniae and other members of the family Mycoplasmatacease were obtained by nucleic acid sequencing techniques known to those of ordinary skill in the art. These sequences were aligned based on regions of sequence homology. Sequence variations among species were then identified from the aligned sequences. These variable regions were then used as target sequences for hybridization assay probes.
• the nucleic acid hybridization assay probes of the present invention can distinguish Mycoplasma pneumoniae from a closely related Mycoplamsa, preferably Mycoplasma genitalium, the nearest phylogenetic neighbor to Mycoplasma pneumoniae.
• hybridization assay probes can also distinguish Mycoplasma pneumoniae from other Mycoplasma, such as Mycoplasma orale, Mycoplasma faucium, Mycoplasma buccale, and Mycoplasma salivarium. These Mycoplasma have been isolated from humans.
• rRNA sequence information was obtained experimentally and from published information. (See, Weisburg et al., J. Bacteriol 171:6455 (1989).) Experimental information was obtained by isolating and sequencing rRNA from various organisms using standard techniques known in the art. More specifically, rRNA sequence information was obtained by first using oligonucleotide primers complementary to conserved regions which vary little between prokaryotic organisms. The primer was then extended using reverse transcriptase and deoxyribonucleotides to produce cDNA. The cDNA nucleic acid sequences were determined using the method of dideoxynucleotide chain termination. (E.g., Lane et al., Proc. Natl. Acad. Sci. USA, 82:6955 (1985).)
• Hybridization assay probes and helper probes hybridize to their target sequence at stringent hybridization conditions.
• Hybridization assay probes are designed to preferentially hybridize to Mycoplasma pneumoniae nucleic acid and helper probes can aid in assay probe hybridization.
• Amplification oligonucleotides aid in the amplification of target sequences. Oligonucleotides acting as helper probes or amplification oligonucleotides do not need to be able to preferentially hybridize to Mycoplasma pneumoniae nucleic acid.
• nucleotide sequences from different organisms were first aligned to maximize homology.
• rRNA molecule there is a close relationship between secondary structure (caused in part by intramolecular hydrogen bonding) and function. This fact imposes restrictions on evolutionary changes in the primary nucleotide sequence causing the secondary structure to be maintained.
• a compensating substitution usually occurs in the primary sequence of the other "strand” in order to preserve complementarity (this is referred to as co-variance), and thus the necessary secondary structure.
• This allows two very different rRNA sequences to be aligned based both on the conserved primary sequence and also on the conserved secondary structure elements. Potential target sequences for the hybridization assay probes described herein were identified by noting variations in the homology of the aligned sequences.
• sequence evolution at each of the variable regions is mostly divergent. Because of the divergence, corresponding rRNA variable regions of more distant phylogenetic relatives of Mycoplasma pneumoniae show greater differences from Mycoplasma pneumoniae rRNA than do the rRNAs of phylogenetically closer relatives. We observed sufficient variation between Mycoplasma pneumoniae and its closest phylogenetic relative, Mycoplasma genitalium, to identify preferred target sites and design hybridization assay probes useful for distinguishing between the nucleic acids of these two organisms.
• Preferential hybridization of hybridization assay probes to their target nucleic acids can be accomplished by choosing the appropriate hybridization assay conditions and proper probe design.
• the stability of the probe:target nucleic acid hybrid should be chosen to be compatible with the assay and washing conditions so that stable, detectable hybrids only form between nucleic acids having highly complementary sequences.
• Manipulation of one or more of the different assay parameters determines the exact sensitivity and specificity of a particular hybridization assay probe.
• Probes should be designed to have an appropriate melting temperature (T m ).
• T m melting temperature
• the appropriate T m can be obtained by varying the probe length and nucleotide composition (percentage of G+C versus A+T).
• the probe length and nucleotide composition should preferably be chosen to correspond to a T m about 2°-10° C. higher than the temperature at which the final assay will be performed.
• the optimal hybridization temperature for an oligonucleotide is approximately 5° C. below the melting temperature for a given duplex. Incubation at temperatures below the optimum temperature may allow mismatched base sequences to hybridize and can therefore decrease specificity.
• the longer the oligonucleotide the more hydrogen bonding between base pairs and, in general, the higher the T m .
• Increasing the percentage of G and C also increases the T m because G--C base pairs exhibit additional hydrogen bonding and therefore greater thermal stability than A--T base pairs. Such consideration are known in the art. (See, e.g., Chapter 11 of Sambrook, et al., supra.)
• a preferred method to determine T m measures hybridization using a hybridization protection assay (HPA) according to Arnold et al., supra entitled “Homogeneous Protection Assay.”
• T m can be measured using HPA in the following manner.
• Probe molecules are labeled with an acridinium ester.
• Probe:target hybrids are formed in a lithium succinate buffer (0.1 M lithium succinate buffer, pH 5.0, 2 mM EDTA, 2 mM EGTA, 10% (w/v) lithium lauryl sulfate) using an excess amount of target.
• the amount of acridinium ester remaining after hydrolysis treatment is proportional to the number of hybrid molecules.
• the remaining acridinium ester can be measured by monitoring the chemiluminescence produced from the remaining acridinium ester by adding hydrogen peroxide and alkali to the solution. Chemiluminescence can be measured in a luminometer (e.g., the Gen-Probe LEADER® I or LEADER® 50). The resulting data is plotted as percent of maximum signal (usually from the lowest temperature) versus temperature.
• the T m is defined as the temperature at which 50% of the maximum signal remains.
• T m may be determined by isotopic methods known to those skilled in the art (see e.g., Hogan et al., supra).
• the T m for a given hybrid varies depending on the nature of the hybridization solution used. Factors such as the salt concentration, detergents, and other solutes can affect hybrid stability during thermal denaturation (see J. Sambrook, et al., supra). Conditions such as ionic strength and the temperature at which a probe will be allowed to hybridize to target should be taken into account in probe construction. The thermal stability of a hybrid nucleic acid increases with the ionic strength of the reaction mixture. On the other hand, chemical reagents which disrupt hydrogen bonds, such as formamide, urea, dimethyl sulfoxide and alcohols, can greatly reduce hybrid thermal stability.
• hybridization assay probe For its target, it is preferable to design probes which hybridize only with target nucleic acid under conditions of high stringency. Only highly complementary nucleic acid hybrids form under conditions of high stringency. Accordingly, the stringency of the assay conditions determines the amount of complementarity which should exist between two nucleic acid strands in order to form a hybrid. Stringency should be chosen to maximize the difference in stability between the probe:target hybrid and potential probe:non-target hybrids.
• Proper specificity may be achieved by minimizing the length of the hybridization assay probe having perfect complementarity to sequences of non-target organisms, by avoiding G and C rich regions of complementarity to non-target nucleic acids, and by constructing the probe to contain as many destabilizing mismatches to non-target sequences as possible. Whether a probe is appropriate for detecting only a specific type of organism depends largely on the thermal stability difference between probe:target hybrids versus probe:nontarget hybrids. In designing probes, the differences in these T m values should be as large as possible (preferably 2° C.-5° C. or more).
• the length of the target nucleic acid sequence region, and accordingly the length of the hybridization probe substantially complementary targeted region, can also be important. In some cases, there may be several nucleotide sequences from a particular target region, varying in location and length, which may be used to design probes with the desired hybridization characteristics. In other cases, one sequence may be significantly better with regard to specificity than another which differs from it merely by a single base. While it is possible for nucleic acids that are not perfectly complementary to hybridize, the longest stretch of perfectly complementary nucleotides generally determines hybrid stability.
• Regions of rRNA known to form strong internal structures inhibitory to hybridization are less preferred target regions. Likewise, probes with extensive self-complementarity should be avoided. If a strand is wholly or partially involved in an intramolecular or intermolecular hybrid it will be less able to participate in the formation of a new intermolecular probe:target hybrid. Ribosomal RNA molecules are known to form very stable intramolecular helices and secondary structures by hydrogen bonding. By designing a probe to a region of the target nucleic acid which remains substantially single-stranded under hybridization conditions the rate and extent of hybridization between probe and target may be increased.
• a genomic rDNA target occurs naturally in a double-stranded form, as does the product of the polymerase chain reaction (PCR). These double-stranded targets require denaturation prior to hybridization. Appropriate denaturation and hybridization conditions are known in the art (e.g., E. M. Southern, J. Mol. Biol. 98:503 (1975)).
• Example of specific stringent hybridization conditions for hybridization assay probes are provided in the examples described below. Additional sets of stringent hybridization conditions can be determined based on the present disclosure by those of ordinary skill in the art. (See e.g., Sambrook, et al., Molecular Cloning: A Laboratory Manual (Cold Springs Harbor Laboratory Press, 1989) at Chapter 11.)
• helper Probes as described in Hogan and Milliman, U.S. Pat. No. 5,030,557.
• Helper probes are sufficiently complementary to their target nucleic acid sequence to form a helper probe:target duplex under stringent hybridization assay conditions.
• the stringent hybridization assay conditions used with a given helper probe are determined by the conditions in which a hybridization assay probe is used to preferentially hybridize to its target sequence.
• Regions of single stranded RNA and DNA can be involved in secondary and tertiary structures even under stringent hybridization assay conditions. Such structures can sterically inhibit, or even block hybridization of a hybridization assay probe to its target region. Hybridization of the helper probe alters the secondary and tertiary structure of the target nucleic acid, thereby rendering the hybridization assay probe target region more accessible. As a result helper probes enhance the kinetics and/or the T m of the target:hybridization probe duplex. Helper probes are generally selected to hybridize to nucleic acid sequences located near the hybridization assay probe target region.
• Helper probes which can be used with the hybridization assay probes of the present invention are targeted to nucleic acid sequences provided by SEQ. ID. NOs: 33, 36, 39, 45, 48, 51, 54, 57, 60, 64, 67, 70, 73, 76 and 79.
• the probes are preferably 12 to 100 nucleotides in length and contain a targeted region of 10 nucleotides of which at least 9 out of the 10 nucleotides are perfectly complementary to a nucleic acid sequence present in the target region.
• helper probes useful in the present invention are those having, consisting essentially of, or consisting of, the following nucleotide sequences (written 5' to 3'):
• RNA equivalents thereto SEQ. ID. NOs: 34, 37, 40, 46, 9, 52, 55, 58, 62, 65, 68, 71, 74, 77 and 80.
• hybridization assay probe and helper probes combinations are used:
• the degree of amplification observed with a set of primers or promoter-primers depends on several factors, including the ability of the oligonucleotides to hybridize to their specific target sequences and their ability to be extended or be recognized by an RNA polymerase. While oligonucleotides of different lengths and base composition may be used, more preferred amplification oligonucleotides have target binding regions of 18-50 bases and a predicted hybrid T m of about 65° C.
• a target nucleic acid sequence present on a nucleic acid molecule can be amplified using an amplification oligonucleotide 5' of the target sequence and an amplification oligonucleotide 3' of the target sequence.
• the preferred target sites for amplification oligonucleotides are regions greater than about 15 bases in length.
• the amplified region, defined by the amplification oligonucleotides, is preferably about 350 bases, and more preferably within 150 bases.
• T m Parameters affecting probe hybridization such as T m , complementarity and secondary structure also affect primer hybridization and therefore performance of the amplification oligonucleotides.
• T m Trigger-to-Stret al.
• amplification can be carried under conditions of lower stringency then diagnostic hybridization assay conditions.
• the degree of non-specific extension can affect amplification efficiency.
• Primers are preferably selected to have low self- or cross-complementarity, particularly at the 3' ends of the sequence. Long homopolymer tracts and high GC content are preferably avoided to reduce spurious primer extension.
• Computer programs are commercially available to aid in this aspect of the design.
• oligonucleotide may be produced by any of several well-known methods, including automated solid-phase chemical synthesis using cyanoethylphosphoramidite precursors (Barone et al., Nucleic Acids Research 12:4051 (1984)), and as described in Sambrook, et al., supra, at ch. 11. Following synthesis and purification of an oligonucleotide, several different procedures may be utilized to determine the acceptability of the oligonucleotide in terms of size and purity. Such procedures include polyacrylamide gel electrophoresis and High Pressure Liquid Chromatography.
• Hybridization assay probes may be labeled with a reporter group by any of several well-known methods (J. Sambroock, et al., e.g., supra).
• Useful labels include radioisotopes and non-radioactive reporting groups.
• Isotopic labels include 3 H, 35 S, 32 P, 125 I, 57 Co and 14 C.
• isotopic labels can be introduced into an oligonucleotide by techniques known in the art such as nick translation, end labeling, second strand synthesis, reverse transcription, and by chemical methods.
• hybridization can be detected by techniques such as autoradiography, scintillation counting, or gamma counting. The chosen detection method depends on the particular radioisotope used for labeling.
• Non-isotopic materials can also be used for labeling and may be introduced internally between nucleotides or at an end of the oligonucleotide. Modified nucleotides may be incorporated enzymatically or chemically. Chemical modifications of the oligonucleotide may be performed during or after synthesis of the oligonucleotide using techniques known in the art. For example, through the use of non-nucleotide linker groups as described by Arnold et al., entitled “Non-Nucleotide Linking Reagents for Nucleotide Probes," EPO application number 88308766.0, publication number 313219, hereby incorporated by reference herein. Non-isotopic labels include fluorescent molecules, chemiluminescent molecules, enzymes, cofactors, enzyme substrates, and haptens or other ligands.
• the hybridization assay probes are labeled with an acridinium ester.
• Acridinium ester labeling may be performed as described by Arnold et al., U.S. Pat. No. 5,185,439 entitled “Acridinium Ester Labeling and Purification of Nucleotide Probes” issued Feb. 9, 1993 and hereby incorporated by reference herein.
• Examples are provided below illustrating different aspects and embodiments of the present invention.
• the examples illustrate methodology by which oligonucleotides having, consisting essentially of, and substantially similar to, a specified nucleotide sequence of a hybridization assay probe, helper probe, or amplification oligonucleotide, can be obtained. These examples are not intended in any way to limit the disclosed invention.
• Probes specific for Mycoplasma pneumoniae were designed by first sequencing prospective target areas using primers complementary to the rRNAs of Mycoplasma pneumoniae (ATCC NO. 15531) and Mycoplasma genitalium (ATCC NO. 33530), or from published 16S sequences. These sequences were compared to determine variable regions.
• the rRNA sequences of phylogenetically near neighbors including Mycoplasma hyopneumoniae, Mycoplasma arginini, Mycoplasma liphophilum, Mycoplasma californicum, Mycoplasma bovigenitalium, Mycoplasma salivarium, Mycoplasma hominis, Mycoplasma arthritidis, Mycoplasma arginini, Mycoplasma pulmonis, Mycoplasma mycoides, Mycoplasma imitans, Mycoplasma iowae, Mycoplasma muris, Mycoplasma pirum, Mycoplasma gallisepticum, and U. urealyticum were also compared to Mycoplasma pneumoniae rRNA to determine variable regions.
• Hybridization assay probes having the following nucleotide sequences are featured in the examples described below:
• the probes were synthesized with a non-nucleotide linker as described by Arnold et al., "on-Nucleotide Linking Reagents For Nucleotide Probes," supra, then labeled with a chemiluminescent acridinium ester as described by Arnold et al., U.S. Pat. No. 5,185,439.
• the reactivity and specificity of the probes for Mycoplasma pneumoniae nucleic acid were demonstrated using a two phase hybridization and separation format (the results shown in Tables 3, 4 and 5) or a single phase homogeneous assay format (the results shown in Tables 2, 6 and 7).
• Results are given in relative light units (RLU), a measure of the photons detected by the luminometer.
• Probes were hybridized to a nucleic acid in a cell lysate, or purified RNA. Purified RNA was obtained as generally described in J. Sambrook, et al., supra. Lysates, especially of Mycobacteria, Gram positive organisms, or yeasts, can be obtained as described by Murphy et al., "Method for Releasing RNA and DNA from Cells," EPO Publication No. 288618, hereby incorporated by reference herein. The following examples describe hybridization assay probes targeted to Mycoplasma pneumoniae rRNA sequences, or the corresponding gene, and their use in a hybridization assay.
• RLU relative light units
• RNA 50 ng was hybridized to probe mixes in 100 ml 0.05 M lithium succinate pH 5, 0.6 M LiCl, 1% (w/v) lithium lauryl sulfate, 10 mM EDTA, 10 mM EGTA at 60° C. for 30 minutes, followed by addition of 300 ⁇ l of 0.15 M sodium tetraborate pH 8.5, 1% TRITON®X-100 at 60° C. for 8-9 minutes. Each sample was tested in duplicate with 0.16 pmol hybridization assay probe and 0.4 pmol helper probe. Acridinium ester signal production was read in a luminometer by injecting 0.1% hydrogen peroxide in 1 mM nitric acid, followed by injection of a 1 N sodium hydroxide solution.
• probes targeted to Mycoplasma pneumoniae nucleic acid readily distinguish Mycoplasma pneumoniae from Mycoplasma genitalium.
• the data in this table are reported in RLU without subtracting background or negative control values. The results of duplicate experiments are reported.
• An acridinium ester-labeled probe having the nucleotide sequence provided by SEQ. ID. NO. 1 was used with unlabeled helper probes having the nucleotide sequences of SEQ. ID. NOs. 9 and 10.
• An acridinium ester-labeled probe having the nucleotide sequence of SEQ. ID. NO. 2 was used with unlabeled helper probes having the nucleotide sequences of SEQ. ID. NOs. 11 and 12.
• An acridinium ester-labeled probe having the nucleotide sequence of SEQ. ID. NO. 3 was used with unlabeled helper probes having the nucleotide sequences of SEQ. ID. NOs. 13 and 14.
• An acridinium ester-labeled probe having the nucleotide sequence of SEQ. ID. NO. 4 was used with unlabeled helper probes having the nucleotide sequences of SEQ. ID. NOs. 15 and 16.
• An acridinium ester-labeled probe having the nucleotide sequence of SEQ. ID. NO. 5 was used with unlabeled helper probe having the nucleotide sequence of SEQ. ID. NO. 17.
• An acridinium ester-labeled probe having the nucleotide sequence of SEQ. ID. NO. 6 was used without helper probes.
• An acridinium ester-labeled probe having the nucleotide sequence of SEQ. ID. NO. 7 was used with unlabeled helper probe having the nucleotide sequence of SEQ. ID. NO. 18.
• An acridinium ester-labeled probe having the nucleotide sequence of SEQ. ID. NO. 8 was used with unlabeled helper probes having the nucleotide sequences of SEQ. ID. NOs. 19 and 20.
• Probes 2, 3, 4, 5, 6, and 7 showed no significant reaction over background signal with Mycoplasma genitalium target.
• the probe mix containing a probe having the nucleotide sequence of SEQ. ID. NO. 8 and the probe mix containing a probe having the nucleotide sequence of SEQ. ID. NO. 1 showed a slight signal over background when combined with 50 ng of Mycoplasma genitalium rRNA under these assay conditions. This amount of purified rRNA corresponds to about 2 ⁇ 10 10 copies of rRNA, or approximately 20 million bacteria.
• This example illustrates the ability of a probe mixture containing acridinium ester-labeled probes targeted to Mycoplasma pneumoniae rRNA to detect various Mycoplasma pneumoniae strains but not other microorganisms in a hybridization and separation assay format.
• This format gives lower background signals than the homogeneous assay format described above and used to obtain the data shown in Table 2.
• the probe mixture contained acridinium ester-labeled probes having the following nucleotide sequences:
• Table 3 presents data obtained using the probe mix against an excess of RNA released from liquid broth cultures containing 10 6 -10 8 organisms.
• hybridization solution containing 0.19 M lithium succinate pH 5, 0.62 M lithium lauryl sulfate, 3 mMEDTA, 3 mMEGTA, and the probe mix was combined with an equal volume of cell lysate (about 100 ng of rRNA) and incubated at 60° C. for one hour.
• Hybrids were then bound to magnetic amine microspheres (Perseptive Biosystems, Inc., Cambridge, MA) in a solution containing 0.19 M sodium tetraborate pH 7.5, 6% (v/v) TRITON®X-100 and washed once in a solution containing 20 mM sodium tetraborate pH 10.4.
• the particle-associated chemiluminescence from the hybridized acridinium ester-labeled probes was measured in a luminometer as described in Example 1.
• the data in Table 3 show that the probe mix indicates the presence of Mycoplasma pneumoniae and distinguishes Mycoplasma pneumoniae from several closely related Mycoplasma, Acholeplasma, Ureaplasma and Spiroplasma species.
• Chemiluminescence was measured in a Gen-Probe LEADER® I luminometer and data are expressed in net Relative Light Units (signal minus the value obtained with a sample containing 1 ng of non-Mycoplasma rRNA). The probe mix exhibited a low level of cross-reactivity to some Mycoplasma isolates.
• the probe mix showed low reactivity to these five isolates. Greater than 10 ng of Mycoplasma these five isolates. Greater than 10 ng of Mycoplasma gallisepticum and Mycoplasma pirum RNA were required to give a positive result. Although the cross-reactivities of three Mycoplasma genitalium RNA's were somewhat higher, there was still a 400-fold difference in reactivity between Mycoplasma pneumoniae rRNA and Mycoplasma genitalium rRNA. Cross-reactivity in clinical specimens is not expected to be detectable above background.
• Table 5 shows that the probe mix, described in Example 2, distinguishes Mycoplasma pneumoniae from twenty-seven bacterial genera representing a phylogenetic cross section of microorganisms using the assay format described in Example 2.
• This example illustrates the use of Mycoplasma pneumoniae hybridization assay probes to detect the products of nucleic acid amplification.
• a Mycoplasma pneumoniae hybridization assay probe of the same sense as the target rRNA nucleic acid was used to detect the products of target nucleic acid amplification.
• Mycoplasma pneumoniae and Mycoplasma genitalium rRNA was separately amplified with primer having the nucleotide sequences of SEQ. ID. NO. 51 and a promoter-primer having the nucleotide sequences of SEQ. ID. NO. 82 containing the promoter sequence 5'-AATTTAATACGACTCACTATAGGGAGA-3' (SEQ. ID. NO. 92) at the 5' end.
• Amplification was performed using a Perkin-Elmer thermocycler as follows: the target nucleic acid was heated to 95° C. for 15 minutes, cooled to 42° C. in 100 ⁇ l of a solution containing 0.3 ⁇ M of the promoter-primer, 0.3 ⁇ M of primer, 50mMTris-HCl, pH 7.6, 25 mM KCl, 17.5 mM MgCl 2 , 20 mMN-acetyl cysteine, 2.5 mM rATP, 2.5 mM rCTP, 2.5 mM rGTP, 2.5 mM rUTP, 1 mM dATP, 1 mM dCTP, 1 mM dGTP and 1 mM dTTP.
• hybridization assay probes targeted to nucleic acid sequences complementary to Mycoplasma pneumoniae rRNA to detect the product from a target amplification procedure.
• This example also illustrates detection of amplified target nucleic acid.
• Nucleic acid from Mycoplasma pneumoniae and Mycoplasma genitalium were amplified by heating to 95° C., followed by 30 rounds of temperature cycling at 55° C. (30 seconds), 60° C. (60 seconds) and 95° C. (60 seconds), followed by seven minutes at 60° C. Amplification took place in 100 ⁇ l of a solution containing 50 mM potassium chloride, 10 mM Tris HCl pH 8.3, 1.5 mM magnesium chloride, 0.25 mM dATP, 0.25 mM dTTP, 0.25 mM dGTP, 0.25 mM dCTP, 2.5 U of Taq polymerase, 1 FM primer SEQ. ID. NO.
• hybridization probes described herein are capable of distinguishing Mycoplasma pneumoniae from its known nearest phylogenetic neighbors.
• complementary oligonucleotide probes can detect the products of nucleic acid amplification procedures.

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